The present invention relates to an air conditioning apparatus for a motor vehicle and, more particularly, to a system for controlling an operation of a compressor included in the apparatus in accordance with engine operating conditions of a motor vehicle.
A prior art automotive air conditioning apparatus is so constructed as to on-off control its compressor within a given range which prevents a cooler operated by the compressor from being cooled off beyond a freezing level. For this purpose, the air conditioning apparatus employs a compressor control switch of the type which is actuated when the temperature at the cooler or in an air flow duct downstream of the cooler drops to a predetermined level or when the pressure of a refrigerant circulated through the cooler drops. However, such a compressor on-off control is carried out with no regard to engine operating conditions or running speeds of a motor vehicle in which the apparatus is installed. When a motor vehicle runs in an urban area, it is repeatedly accelerated, decelerated and stopped as indicated in FIG. 1a in which P.sub.s shows a stop period, P.sub.a an acceleration period, P.sub.c a constant speed cruising period and P.sub.d a deceleration period. Since the compressor is controlled with its relation with the engine operating conditions or vehicle running conditions left out of consideration, it is often activated during accelerations P.sub.a or deactivated during decelerations P.sub.d. This degrades the general energy efficiency, forces the engine to bear excessive loads and deteriorates fuel economy of the engine.